Beamforming is a signal processing technique used to create directional or spatial selectivity of signals sent to or received from an array of sensors or an array of antennas. These arrays can be found in a variety of devices that transmit and receive electromagnetic or acoustic waves. Accordingly, this technique has numerous applications in radars, sonars, seismology, wireless communications, radio astronomy, acoustics, medical, and industrial ultrasound technologies.
In conventional beamforming, a source may transmit a wave that propagates and arrives at sensors of an array at different times, depending on the source orientation and the array geometry. To synchronize the arrival times throughout the array, outputs of the sensors of the array can be delayed and then aggregated to provide a beamforming output. In some cases, the outputs of the sensors of the array can be applied in different weights (to decrease echo, for example). The beamforming process can also be used to detect and estimate the signal-of-interest at the output of an array of sensors or antennas by means of optimal spatial filtering and interference rejection.
The array of sensors can include, for example, an array of microphones or an array of ultrasound piezoelectric crystals for receiving acoustic sound waves or an array of antennas for receiving electromagnetic waves. A beamforming technique can be used to map sound waves (e.g., in case of a sonar system), evaluate sound waves, or to augment sound waves using modifying and/or compensating delays and/or applying various weights.
FIG. 1 shows a block diagram of an example conventional beamformer 100, which is also known in the prior art as a “delay-and-sum beamformer.” As can be seen from FIG. 1, the beamformer 100 includes an array of sensors 105A-105Z, which may include microphones, antennas or other signal generating devices. The sensors 105A-105Z are operatively coupled to analog-to-digital (A/D) converters 110A-110Z, accordingly. The A/D converters 110A-110Z receive analog signals generated by the sensors 105A-105Z and generate corresponding digital signals for further processing. The digital signals from each A/D converter 110A-110Z are fed into a plurality of delaying units 115A-115Z. Further, the delaying units 115A-115Z delay digital signals received from the A/D converters 110A-110Z at slightly different times so that every signal may reach output at substantially the same time. In narrow-band systems, the time delay may be equivalent to “phase shifting” so that the resulting output signal, when all shifted signals are combined, is referred to as a “phased array signal.”
Further, in the beamformer 100, the signals from every delaying unit 115A-115Z may be amplified by applying different “weights.” Different weighting patterns (e.g., Dolph-Chebyshev) can be used to achieve the desired sensitivity patterns, improve signal-to-noise ratio, reduce blasting, or improve filtering. The weights can be applied by a plurality of multipliers 120A-120Z. Thus, both the delaying units 115A-115Z and the multipliers 120A-120Z can perform conditioning of the signals derived from the sensors 105A-105Z depending on a particular application.
With continuing reference to FIG. 1, the conditioned signals outputted from the multipliers 120A-120Z may be supplied to a summer 125. The summer 125 combines all signals into a single phased array output signal, which can be then analyzed, processed, played, or in any other way utilized by another system or apparatus. The beamformer 100 may include hardware components, software components, or a combination thereof.
In various applications, the number of input signals, i.e., signals generated by the sensors 105A-105Z, may differ. For example, in simple sonar systems, 16 sensors and, correspondingly, 16 input signals can be used; however, in more complex ultrasound testing systems, there can be hundreds of input signals. In such complex cases, beamformers may use a large number of A/D converters, delaying units, and multipliers in order to process such a big number of input signals. However, due to conventional limitations of hardware components, the number of input signals that can be combined by a conventional summer is typically less than one or several tens. To address this problem, beamformers may be equipped with more than just one summer.
FIG. 2 shows a block diagram of an example conventional beamforming system 200, which includes a plurality of beamformers 205A-205Z. As shown in the figure, the beamformers 205A-205Z are coupled in series such that a first output signal of a first beamformer 205A is supplied to a second beamformer 205B, in which the first output signal is combined with a second output signal, and so forth until the last beamformer 205Z generates a phased array output signal.
FIG. 3 shows a block diagram of another example conventional beamforming system 300, which includes a plurality of beamformers. In this example of conventional system 300, each beamformer 310A, 310B, and so forth include more than one summer. As shown in FIG. 3, the delaying units 115A-115Z may generate a plurality of signals delayed by various time periods and then separately supplied to multipliers and subsequently to summers 305A-305N so that each summer 305A-305N combines signals to which the same weights were applied. The beamformers 310A, 310B, and so forth are interconnected such that the summers 305A-305N of each beamformer 310A, 310B and so forth are interconnected in series as shown in FIG. 3. Thus, the combined signals of the first summers 305A pertaining to the beamformers 310A, 310B, and so forth are summed together and outputted to a post-processing unit 315. Similarly, the summed signals of the second summers 305B and summed signals of the remaining multipliers are outputted into the same post-processing unit 315 as shown in FIG. 3. The post-processing unit 315 may process all such signals to generate a desired phased array output signal for further analysis.
Shortcomings of the conventional beamforming systems shown in FIG. 2 and FIG. 3 may include the inability to adapt to various purposes because these beamforming systems may be only configured to process a predetermined number of signals generated by the sensors 105A-10Z. Thus, the conventional beamforming systems may require significant reconfiguration for varying purposes and numbers of sensors.